Loud speaker



-J. E. sED'EH'oLM.

LOUD SPEAKER 2' Sheets-Sheet Filed Feb. 23, 1928 l In Venor Jal-1N ESELUEBHQ/ M Dec. 11, 192s.

A 1,695,126 J. E. SEDERHOLM LOUD SPEAKER Filed Feb. 23, 1928 5V I V 2 Sheets-Sheet 2 A Inventor JQHN EQEDERHo/ M l Avvor'ney Jratentgcl Dec. 11, 1228.

UNITED .STATES OFFICE.

JOHN E. SEDEEHOLM, OFQST. PAUL, MINNESOTA, yAssIeNoR "ro AMERICAN 'nors'i a v:ennemi: COMPANY, OP sr. PAUL, MINNESOTA, A PARTNERSHIP ooMPosED or E.V J. JOHNSON AND W. o. WASHEUEN.

i vLOUD SPEAKER.

Application .filed February 23, 1928. Serial No.`256,341.

This invention relates to improvements in vloud speakers, the main object of the inyention being to clearly reproduce all sounds with the maximum` of volumeand cl'earness.v

Another object is to-produce a loud speaker v which will clearly produce sounds with `a maximum volume, and with a minimum 'expenditure of electrical energy, and which will,

operate in this improved manner with any m type of radio set, to clearly reproduce mixtures of vibrations. y

In order to-understand the problems of a device of this-kind, it is to be known that the ordinary speakers have a natural `vibratory period of from three thousand to seven thousand vibrations per second. When the speaker responds to vibrations which correspond ,closely to these natural periods, blasting ordistortion results so that itis practically impossible toy transmit a mixture of vibrations with clearness and proper volume.

' n `Some of the instruments `of an orchestra will be taken as an example,a tuba, for example,

having' four hundredl vibrations per second,

alnother instrument having five hundred Iifty vibrations per second, the next seven hundred, the next eight hundred twenty-five, and so on up to four thousand vibrations per second. The various vibrations are being relceived slmultaneously and' 1n some bands the` total' vibration may reach fivey hundred fthoimand per second at any given time.

Features of the invention include the broad idea of using a sti armature and furnishing suicient energyto properly operate the same,

i along with all details of construction for accomplishing all results. l

Therefore, the vibrating element, or vi` brator should have a naturalk vibratory pe- 40 -riod equal to or,considerablyabovethat of the human ear. The present invention provides a vibrator whose natural period is far above that of which the ear is capableof re-` sponding, and which has been found to propf erly respond tothe high vibratory frequen- L cies of a mixture of varying frequencies, as,

for example, produced by the band or orchestra above mentioned. l

The diiiiculty heretoforey has been to prop-v erly operate.fwith that tamount 4of electric .power obtainable in a radio set, a vibrator responsive to frequencies suiciently high to obtain the above result. By providingI a partially closed magnetic circuit which acts to .permanent magnet.

conserve the electric energy am able to oper ate a high `frequency lvibrator inthe manner outlined. i

Although the details of construction of the i i device and combinations and sub-combina-V tions are claimed, there is no intention to limit the invention to these details, because` the invention broadly contemplates the conservation of magnetic force in a manner to operate a stiff vibratoior a vibrator which can respond to vibrationsof unusually high frequencies, as well as to vibrations of`lower frequencies.

Advantages of the invention will be set 'forth in the description of the drawings form- `.inga part of this application, and in said *In'agnetic unit in front View with the connector for the vibrators and cone shown in sec- Atlon;

Figure 3 isa central vertical section of FiUure-2; and 1 Figure .4 is a detailed ,v vertical' section through the coil approximately on line 4--4 of Figure 3. f 1

The device provides a support 1 and a cone 2 having its periphery resting against the support. Intermediately of, the cone and support, and attached to the support at one point as by screw 3, is a frame generally indicated at 4 and having a thin resilient portion 5 and a horizontal shelf portion 6. yThe frame provides side `portions 7 between and screw bolt l0 is passed through 'the walls 7 to clampingly secure the element 9 between these walls. A screw l2 accessible from the outer side of the support engages the frame 4 to adjust it, against the tension of element 5. As now constructed the U-'shaped element is made `of tungsten steel .which forms the The -lower leg 9 rests ilatly against the shelf-like portion 6 and has its front edge flush with'the `front edge ofthe f shelf 6. The arm 14 lies directly above the arm 9 and is of less length as best shown'in Figure 3. Mounted upon the upper surface of the outer end of this lower arm is .a block .20 perpendicularly arranged,land having` an p suitable' screws 31.' The strip 29 is secured opening 21 therethrough, adjacent its top portion. Within this'opening: is fitted a coil 22 having a core 23. T e core projects rearwardly as shown in Figure 3, and its front lportion is spaced inwardly from the front surface of the block 20. The rea-r surface of the coil engages the free end of the arm 14 and lalso abuttingly engages a block 2 4, said'. block having an opening 25 receiving an extension ofthe core 23. vThis extension passes partly through the bore 25 and is secured at 26, as by soldering, the soldering closing the bore 25 as shown. Onthe top of the block `is arranged a metallic strip orbar 29, u on which are mounted binding posts 30 heldp by uponthe block 24 and the block is secured to thearm 14 by screws 35 having retain- `ing nuts 34. Q' Connections of respective bind-'V :ing osts with the coil are indicatedl at 3 6.

'The inding screws4 are shown at 37. It will beunderstood that suitable electrica-l power4 connections are provided to energize the coil.

To th outer Vface of the block 20 isattacheda `relatively thick vibratori-'4 In the device as at resent made this vibrator` has a thickness o about one-sixteenth of an inch. The vibrator has a circular head Vportion 40 and a reduced portion 41 attached by a screw 42 tothe block 20. A washer 43 is interposed as shown so .that the, clearance is about five one-sixteenths one-thousandths of an inch. Of course, this clearance has been exaggerated in the drawing.V Centrally of the disk-likeportion 40 is secured 'arod 45, which is about one and ones'ixteenth linches in length and about three sixty-fourths of an inch in diameter, the diprovides and can successfully operate, a v1- ameter of the outer end 46 of the rod is apand about `onehalf inch in length, and passes through an opening 47 inthe cone 2. Clamping means, including elements 49 and nuts-50 secure the cone to the rod. The rod at the 'inner end may be connected either by screwing or soldering 'It is` assumed to be soldered, in this instance. In the vdevice as at present made the' length of the vibrator from the axis of the screw 42-to theaxis of thearod is approximately'. one and nine-thirty-seconds inches. The diameter of the head portion 40 is approximately. thirteen-sixteenths of an inch, while the opening 21 of the block is approximately three-fourths of an inch in di" ameter.v The Width of the block is about one finch, its thickness about three-eighths of an inch, and its length over-all is about two and inches. -The measurements are only given to show the approximate proportions of the device as now made land operating. The tungsten steel U-shaped element has a width of about `one inch, and a thickness of about three-sixteenths of an inch. The lower arm from center of curvature outwardly has a length of about two and one-fourth inches, while the upper arm from the center coil requires more power for operation. The

of curvature outwardly has a len th of about one and -ive-eighths inches. he length. over-all before bending is about five and seven-eighths inches. The vertical distance betweenthe axis of the adjusting screws 12 and the axis of the attaching screw 3 is substantially tive inches. I

The movement of the frame in direction ofA the arrow A obtains a close adjustment of the armature,n while a movement in direction of the arrow B obtains an opposite adjustment. It will be understood that a greater distance-spacing of the armature from the frequency of` the' present armature is estimated to be from eleven to `fifteen thousand. f

' The angle of taper of the cone is twenty degre'es which is' found tofgive the best results.

Th'e periphery of the cone is spaced inwardly from the inner surface of the peripheral 85. wallvlavof the cone about three-thirty-seconds of an inch. n

It will be seen that a portion of the coil is surrounded and enclosed by theelement 20, as the outer pole piece connected to the permanent U-shaped magnet, and thus there is provided, through elements 9, 14, 24, 23, 41, 20, a complete magnetic circuit. Thus a practically closed magnetic circuit is rovided, a portion of which incloses .the coil and prevents stray or wasting of' magneticener .It will be noted therefore that substantia ly y all the magnetic circuit is through metal. It will be also noted that the conducting element for the magnetic circuit is placed outside the coil as well as within it. l

It will be noted that the present invention brator whose natural period is far above that,

of which the human ear is capable of detecting or responding, and which therefore will properly respond to high vibratory frequencies or mixtures of vibrations of var ing fre# quencies, as, for example, produced y a full orchestra or band. Heretofore it has been 1 10 impossible'to properly reproduce the combined frequencies of a plurality of different instruments, because of the lack of selectability of vibrating elements and its inability to respond to the high frequency. effects produced by added effects of different instru- 4ments with such varying frequencies.

It will be noted that the vibrator has more than the ordinary stiffness, and it 1s possible to operate a vibrator of this stiffness because of conservation `of magnetic forceby. means of a practically closedmagnetic circuit.

- Referring to Figure 1, ad]ustment of the .frame in direction' of the arrow A will cause the vibrator to approach the magnetic` coil. Adjustment in direction of the arrow B will cause the vibrator to recede from the magnet. This is true because the vibrator is connected by the element 45 with the cone and when the frame is moved in the direction B and the vlbraten is held from movement, as the result justments, variations of pressure between the periphery of the cone with the support. y

The permanent lmagnet is formedY from s magnetic steel, in this case tungsten alloy. The element is of soft iron or as ordinarily, termed, of `magnetic' iron. This magnetic iron is not capable of becoming a Apermanent magnet but is capable of responding to changes in the magnetic ield and of intercepting, absorbing and distributing magnetic energy, While at the same time oil'ering little electrical resistance. The function of the permanentmagnet is to maintain the armature or vibrator under tension, and the function of the soft or magnetic iron element, as

a portion of the magnetic circuit, is to absorb magnetic energy which would otherwise be lost-. f

It will thus be seen that a device is provided Which comprises a practicallypclosed 1. circuit including a permanent magnet and a section of magnetic iron spaced Jfrom one pole of the magnet in a manner to form a gap along with a coil embedded in the magnetic iron section and projecting. across the gap and having. a core connected at one end withone pole of the permanent magnet along with a vibrator operatively opposed to the opposite end of the core and mounted upon the magnetic iron section.

I claim as my invention:

l. A frame, a permanent magnetsecured tothe frame, a block secured to the permanent magnet and having a bore extending there- K through, a coil fitted within the bore and having a core attached to the magnet, said magnet, core and-block constituting a partially` closed magnetic circuit,a'nd avibrator attachedto the block and opposed to the core.

2. A,unit for the purpose described, comprising a frame having a resilient portion for attachment to a support to permit a swinging motion-of the frame, a permanent magnet secured tothe frame, a block secured to the permanent magnet and having a bore extending therethrough, a coil fitted Within the bore and having a core attached to the magnet, said magnet, core and blocltl consti-` tuting apartially closed magnetic circuit and a vibrator attached to vthe block and opposed` to the bore and core. A

3. A device of the-class described comprising a support, a frame swingingly attached to the support, a permanent magnetI mounted on the trame, a block mounted uponone 'portion of the permanent magnet, a coil embedded in the block and having a core connectedzwith another portion of the permanent magnet all in a manner to provide a partially closed magnetic circuit, and a vibrator carried by the block and arranged to be operable.

,12e lI?,

by the magnet, the cubical "content of the metal of the block being substantially greater thanv that of any other portion oft-the magnetic circuit.- j

4. Al support, a cone engaged against the support, a frame attached to the support to permit a swinging motion, means for swingingly adjusting the iframe,4 a permanent magnet' secured to the frame, a block secured to the permanent magnet and having a bore eX- tending therethrough, a coil fitted within the bOre and having a core attached to the'` magnet, said magnet, core and block constituting a partially closed magnetic circuit, a vibrator attached to the block and opposed to the core, a stiff connection linking the vibrator and cone, and electrical means for energizing the coil, and movement ofthe frame toward andv awayV from the support acting to adjustably space the vibrator with. respect to the-core.

5. A device of the class described comprisu ing a support, a frame swingingly attached to the support, means for adjustably swingf' ing the frame, a permanent magnet mounted on the frame, a block carried by the permanent magnet, a coil embedded in the'block and having a core connected with the permanent magnet all to provide a partially closed magnetic circuit, a vibrator operable by the magnet, a cone having itsperiphery engaged or engageable With the support, means connecting the vibrator and thev cone, the arrangement being su'ch that adjustment of the frame varies the spacing of the vibrator with respect to the core. f

6. A device of thel class described comprising a support, a frame resiliently swingingly attached'to the support, means for adjustably swinging the frame, a permanent magnet' mounted on the frame, a block carried by the permanent magnet, a coil embedded in the block and having a'core connected with another portion of the permanent magnet all to provide a partially closed magnetic circuit, a relatively stiff vibrator carried by the block and operable by the magnet, a cone engaged with the support, a stiff connection between the vibrator andthe cone, the arrangement lbeing such that thel frame lies between the support and the cone, and such that adjustment of the framein one direction' acts to vary the spacingof the vibrator With respect to the core. e

7. A device of the class described coinprising a support, a cone engaged against the support, a frame adj-ustably securedto the support and having mounted thereon an electro-magnet .and a vibrator operable'by the magnet, a connection between the Vibrator and the cone, and means for" adjusting the 3' frame, the arrangement being such that if the fram-e is moved in one direction thewvibra.- tor is caused to approach the magnet and pressure engagement of the cone with the frame is increased and when moved in an opposite direction the vibrator is caused to recede from themagnet and the pressure of the cone with thevba'se is decreased.

8.- Asuppor't a cone having its periphery engaged aganstlthe support, a Vframe having a resilient portion attached to the support to "permit a swinging motion of the frame, the

magnet, said magnet, coreand block constituting a partially closed magnetic circuit, a relatively stiff vibrator attached to the block and having a portion opposed to the bore and core and overlapping' the bore, and a stiff.

' connection linking the vibrator and cone, the

axes of the cone, core, coil and connector be-,v ing substantially coaxial, and electrical means for energizing the coil, said frame being disposed betwen the support and the cone, and adjustment toward and away fromthe support acting to adjustably space the vibrator with respect to the core. n

9. A device of the class described comprising a practically closed circuit including a permanent magnet and a section of magnetic iron vspaced from one pole of the permanent magnet to form a gap, a 'coil embedded inthe magnetic iron section, and projecting across the gap and having a core yconnected at one end with one end of the` permanent magnet, and a vibrator operatively opposed to the opposite end of the core and mounted -upon the magnet iron section.

l0. A device of the class Adescribed comprisling a permanent magnet, a block of magnetic iron connected with one ole of the permanent magnet and spaced rom the other 4pole to form a gap, a coil embedded in the magnetic iron and projecting across the gap, andhaving a core having oneY endxconnecting with that-pole of the permanent magnet which is spaced from the magnetic iron block,

and a vibrator operatively opposed to the other end of the core and mounted upon. said block. p

In witness whereof, I have hereunto set my hand this 20th day of February, 1928.

JOHN E. sEDERHoLM. 

